1. Field of the Invention
The present invention relates to substituted diphenyls of formulae I and II: ##STR2## which can be additionally mixed with substituted diphenyls of formulae III and IV ##STR3## and their use as heat transfer fluids. In the formulae R.sub.1 stands for hydrogen or ethyl, R.sub.2 for ethyl, R.sub.3 for methyl and R.sub.4 for the benzyl radical.